A method for optically shaping a product master model is known (see JP-A 56-144478 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") and JP-B 2-38422 (the term "JP-B" as used herein means a "Japanese patent publication")). It is also known that a mold (such as a simple mold) is produced by a resin molding method using this model.
The prior art process of producing a mold by a resin molding method will be explained with reference to FIG. 2. FIG. 2(A) shows a state that a model 101 and a parting line jig 103 are to be combined and FIG. 2(B) shows a state that they are combined. This model 101 is optically shaped. The parting line jig 103 is formed by machining, hand finishing or the like.
Thereafter, as shown in FIGS. 2(C) and 2(D), the combined model 101 and parting line jig 103 are surrounded by a frame 105 (such as an acrylic plate), and a cavity mold 107 is formed on the parting surface 111 of the model 101 and the parting surface 131 of the parting line jig 103 by a resin molding method (using, as a resin, epoxy resin containing aluminum powder or the like), and cured. Then, as shown in FIG. 2(E), the frame is removed, the combination is turned upside down, and the parting line jig 103 is removed. Thereafter, a drill hole (dowel hole 175) for aligning a core mold with a cavity mold is formed in the parting surface 171 of the cavity mold 107.
Subsequently, as shown in FIGS. 2(F) and 2(G), an assembly of the model 101 and the cavity mold 107 is surrounded by a frame 105, a release agent is applied to the inner surface 115 and parting surface 111 of the model 101, and a core mold 108 is formed on these surfaces by a resin molding method, and cured. Thereafter, the core mold 108 and the cavity mold 107 are separated from each other to remove the model 101. As shown in FIG. 2(H), both molds are combined, bound together by a constraint jig 109 and heated to complete a mold.
In the prior art process of producing a mold, it is only a master model which is optically shaped, and a mold is fabricated through a process for transcribing a model, such as gypsum casting, spray depositing or the like in addition to the above-described resin molding. Heretofore, no photocured resin is available which has satisfactory properties as a mold material and hence, it has been considered that it is impossible to fabricate a mold itself by an optical shaping process.
The prior art method for producing a mold by a transcription process involves the following problems.
(1) The preparation of a master model is required and it takes time and labor. PA0 (2) When a mold is fabricated by transcribing a master model, dimensional accuracy and shape accuracy are deteriorated by transfer. PA0 (3) The transcription of a master model takes time and labor. PA0 (4) The transcription of a master model requires the skills of an expert. For example, the skills are required for determining the parting surface, manufacturing a parting line jig, controlling the temperature of a resin, mixing and defoaming. PA0 (5) The mold manufacturing process is needed additional steps due to preparation of a master model and the transcription works.